1. Field of the Invention
The present invention relates to a single crystal SiC composite material for producing a semiconductor device, and a method of producing the same, and more particularly to a single crystal SiC composite material for producing, for example, a high-temperature or high-frequency device, or a radiation resistant device such as a light-emitting diode, an X-ray optical element, a switching element, an amplifying element, or an optical sensor, and also to a method of producing such a single crystal SiC composite material.
2. Description of the Prior Art
SiC (silicon carbide) is superior in heat resistance and mechanical strength, and has good resistance to radiation. In addition, it is easy to perform the valence control of electrons and holes by doping an impurity. Moreover, SiC has a wide band gap (for example, single crystal 6H-SiC has a band gap of about 3.0 eV, and single crystal 4H-SiC has a band gap of 3.26 eV). Therefore, it is possible to realize a high-temperature property, a high-frequency property, a dielectric property, and a radiation resisting property which cannot be realized by existing semiconductor materials such as Si (silicone) and GaAs (gallium arsenide). SiC is expected to be the material for the next-generation of semiconductor devices, and studies for a practical use of SiC are being vigorously conducted.
As means for effectively using such excellent properties of SiC as a material for producing a semiconductor device, conventionally, known is a method in which single crystal cubic SiC (xcex2-SiC) is epitaxially grown on a single crystal silicon substrate by the chemical vapor deposition method (heteroepitaxial growth method), thereby obtaining a single crystal SiC material for producing a semiconductor device.
With respect to a single crystal SiC material which is produced by using single crystal silicon as a substrate and epitaxially growing single crystal SiC on the surface of the substrate by the heteroepitaxial growth method as described above, a single crystal SiC material having a larger area can be easily obtained in a large amount and in an economical manner as compared with a material which is produced by another conventional production method such as the sublimation recrystallization method or the improved sublimation recrystallization method. Therefore, the production method is rational and economical. On the other hand, single crystal silicon which is used as a substrate for such a single crystal SiC material has a melting point as low as 1,400xc2x0 C. Therefore, the substrate is unstable. In a process of mounting a semiconductor device which is performed at a high temperature of 1,500xc2x0 C. or higher, such as high temperature annealing in the case of doping of P- or N-type impurities, for example, a silicon substrate vanishes, or, even when a silicon substrate does not vanish, the thickness is extremely reduced. Consequently, it is difficult to ensure the thickness and the strength which are requested in the use and handling of a material for producing a semiconductor device. As a result, there arises a disadvantage that warpage or deformation easily occurs in a semiconductor device which is produced from a single crystal SiC material.
Most of single crystal SiC films grown on silicon substrates by the heteroepitaxial growth method are thin or have a thickness of several xcexcm or smaller. The thickness of such a single crystal SiC film is insufficient for allowing the film to be used as it is in a production of a semiconductor device. In order to use such a thin single crystal SiC film in a production of a semiconductor device, therefore, the single crystal SiC film grown on a silicon substrate must be cut off from the silicon substrate, and the thin single crystal SiC film which has been cut off must be transferred onto another substrate which is stable in thickness and strength, and then produced into a predetermined semiconductor device. However, the cutting off of a thin single crystal SiC film of a thickness of several xcexcm at the maximum from a silicon substrate, and the transfer of the thin single crystal SiC film which has been cut off to another substrate cause increase of the number of production steps, and are actually impossible to be implemented.
The invention has been conducted in view of the above-mentioned circumstances. It is an object of the invention to provide a single crystal SiC composite material for producing a semiconductor device, in which the thickness and the strength required in production of a semiconductor device can be ensured, and lattice defects and micropipe defects due to impurity doping seldom occur to enable a high-quality and accurate semiconductor device to be produced, and a method of producing a single crystal SiC composite material for producing a semiconductor device, which can produces such a material at a very high efficiency.
In order to attain the object, in a single crystal SiC composite material for a semiconductor device of a first aspect of the invention, a single crystal SiC film is stacked and bonded via a film-like SiO2 layer onto a surface of a polycrystalline plate consisting of Si and C atoms in a closely contacted manner, and single crystal SiC is grown on the polycrystalline plate by a heat treatment conducted on the composite member.
In a method of producing a single crystal SiC composite material for a semiconductor device for a second aspect of the invention, a single crystal SiC film is stacked and bonded via a film-like SiO2 layer onto a surface of a polycrystalline plate consisting of Si and C atoms in a closely contacted manner, and the composite member is then heat-treated, whereby single crystal SiC in which the crystal is transformed in the same orientation as the single crystal of the single crystal SiC film is integrally grown on the polycrystalline plate.
According to the first and second aspects of the invention, having the above-mentioned characteristic configuration, the polycrystalline plate consisting of Si and C atoms and having heat resistance similar to that of single crystal SiC, and the thin single crystal SiC film are stacked and bonded together in a closely contacted manner while interposing the SiO2 layer having a low thermal conductivity between the plate and the film, and the composite member is then heat-treated. Therefore, the polycrystalline plate serving as a device substrate is prevented from vanishing or thinning in a thermal treating process, and also in a production process of a semiconductor device conducted at a high temperature, such as high temperature annealing, whereby the thickness and the strength which are requested for a material for producing a semiconductor device can be stably ensured. Consequently, an accurate and high-quality semiconductor device which is free from warpage and deformation can be produced.
While impurities are prevented by the intermediate SiO2 layer from entering from the atmosphere into the bonding interface during the heat treatment, the intermediate SiO2 layer is thermally decomposed into Si and O2 as the heat treatment advances. The thermally decomposed O2 escapes to the outside with floatingly diffusing in the intermediate layer region. On the other hand, single crystal SiC can be integrally grown on the polycrystalline plate by the solid phase growth in which the thermally decomposed Si atoms, and Si and C atoms that sublime from the surface of the polycrystalline plate are rapidly diffused and moved toward the single crystal SiC film which is maintained at a lower temperature, to be rearranged in accordance with the single crystal orientation of the single crystal SiC film. According to this configuration, it is possible to attain effects that a single crystal SiC composite material for producing a semiconductor device which is thick and has a high quality can be efficiently produced, and that the quality of a semiconductor device which is produced by using the material can be improved.
In the single crystal SiC composite material for a semiconductor device of the first aspect of the invention, and the method of producing a single crystal SiC composite material for a semiconductor device of the second aspect of the invention, a member which is produced by stacking a single crystal SiC film that is produced on an Si substrate by a heteroepitaxial growth method, via the SiO2 layer onto the surface of the polycrystalline late in a closely contacted manner, bonding the single crystal SiC film to the polycrystalline plate by a heat treatment on the composite material, and removing away the Si substrate under the bonded state by at least one of hydrofluoric acid and nitric acid is used as the composite member. According to this configuration, a single crystal SiC film itself which is requested to have a large area in order to obtain a composite material that is applicable to the production of semiconductor devices of various sizes can be easily produced in a large amount and in an economical manner. Therefore, a single crystal SiC composite material for producing a semiconductor device which is a final product can be increased in size and reduced in production cost.
It is most preferable to use an SiC polycrystalline plate which is produced into a plate-like shape by a thermal chemical vapor deposition method (hereinafter referred to as a thermal CVD method) wherein mixture of impurities in the production process is performed at the minimum level, as the polycrystalline plate which is used in the single crystal SiC composite material for a semiconductor device of the first invention, and the method of producing a single crystal SiC composite material for a semiconductor device of the second invention. Alternatively, an SiC sintered member having heat resistance similar to that of single crystal SiC may be used so that vanishing and thinning do not occur in a thermal treating process (in a temperature range of 1,850 to 2,000xc2x0 C.) on the composite material, and also in a production process of a semiconductor device.
As the SiO2 layer used in the method of producing a single crystal SiC composite material for a semiconductor device of the second invention, a member may be employed which is formed into a film-like shape by one of application of SiO2 powder or a silicon compound containing silicon oil, silicon resin, or silicon grease, and thermal oxidation of the single crystal SiC film and/or the surface of the polycrystalline plate. Among these means, means for applying powder or the like which requires a smaller number of production steps and can be performed by simple works is most preferably used.
Other objects and effects of the invention will be clarified in an embodiment which will be described below.